Niemann–Pick disease, type C

Niemann–Pick disease, type C
Classification and external resources
Specialty	endocrinology
ICD-10	E75.2 (ILDS E75.230)
ICD-9-CM	272.7
OMIM	257220 601015 607623 607625
DiseasesDB	33390
eMedicine	derm/699
MeSH	D052556
GeneReviews	Niemann-Pick Disease Type C
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Niemann–Pick type C is a lysosomal storage disease associated with mutations in NPC1 and NPC2 genes. Niemann–Pick type C affects an estimated 1:150,000 people. Approximately 50% of cases present before 10 years of age, but manifestations may first be recognized as late as the sixth decade.

Niemann–Pick type C is biochemically, genetically and clinically distinct from Niemann–Pick Types A or and B. In Types A and B, there is complete or partial deficiency of the lysosomal enzyme called acid sphingomyelinase. In Niemann–Pick type C, the protein product of the major mutated gene NPC1 is not an enzyme but appears to function as a transporter in the endosomal-lysosomal system, which moves large water-insoluble molecules through the cell. The protein coded by the NPC2 gene more closely resembles an enzyme structurally but seems to act in cooperation with the NPC1 protein in transporting molecules in the cell. The disruption of this transport system results in the accumulation of cholesterol and glycolipids in lysosomes.

Cholesterol and glycolipids have varied roles in the cell. Cholesterol is a major component of cell plasma membranes, which define the cell as a whole and its organelles. It is also the basic building block of steroid hormones, including neurosteroids. In Niemann–Pick type C, large amounts of free or unesterified cholesterol accumulate in lysosomes, and leads to relative deficiency of this molecule in multiple membranes and for steroid synthesis. The accumulation of glycosphingolipids in the nervous system has been linked to structural changes, namely ectopic dendritogenesis and meganeurite formation, and has been targeted therapeutically.

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